Techniques for LIF placement in SAN storage cluster synchronous disaster recovery

ABSTRACT

Improved techniques for disaster recover within storage area networks are disclosed. Embodiments include replicating a LIF of a primary cluster on a secondary cluster. LIF configuration information is extracted from the primary cluster. A peer node from a secondary cluster is located. One or more ports are located on the located peer node that match a connectivity of the LIF from the primary cluster. One or more ports are identified based upon one or more filtering criteria to generate a candidate port list. A port from the candidate port list is selected based at least upon a load of the port. Other embodiments are described and claimed.

RELATED APPLICATION

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 15/933,519, filed on Mar. 23, 2018 and titled“TECHNIQUES FOR LIF PLACEMENT IN SAN STORAGE CLUSTER SYNCHRONOUSDISASTER RECOVERY,” which claims priority to and is a continuation ofU.S. patent application Ser. No. 14/530,070, filed on Oct. 31, 2014 andtitled “TECHNIQUES FOR LIF PLACEMENT IN SAN STORAGE CLUSTER SYNCHRONOUSDISASTER RECOVERY,” which claims priority to U.S. ProvisionalApplication No. 61/916,177, filed Dec. 14, 2013, which are incorporatedherein by reference.

BACKGROUND

A storage cluster may include one or more virtual storage servers, orVservers, which may be used to serve data to one or more host devices,or clients. A Vserver may contain one or more data volumes and one ormore logical interfaces, or LIFs, through which it may serve data to oneor more host devices. A Vserver may securely isolate shared virtualizeddata storage and network, and may appear as a single dedicated server toits clients over storage area network. A cluster may include at leastone Vserver to serve data, but many more Vservers may be used in somecases. For example, multiple Vservers may coexist in a single clusterwithout being bound to any node in a cluster. When a cluster fails dueto a disaster, for example, data may be unavailable to the one or morehost devices. Thus, a need exists for techniques to provide fast andefficient disaster recovery operations in the case of failure clusterwide failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a storage area network.

FIG. 2 illustrates an embodiment of a logic flow.

FIG. 3 illustrates an embodiment of a storage area network.

FIG. 4 illustrates an embodiment of a logic flow.

FIG. 5 illustrates an embodiment of a storage area network.

FIG. 6 illustrates an embodiment of a storage area network.

FIG. 7 illustrates an embodiment of a storage area network.

FIG. 8 illustrates an embodiment of a storage area network.

FIG. 9 illustrates an embodiment of a storage area network.

FIG. 10 illustrates an embodiment of a storage medium.

FIG. 11 illustrates an embodiment of a computing architecture.

FIG. 12 illustrates an embodiment of a communications architecture.

DETAILED DESCRIPTION

Various embodiments may be generally directed to techniques for storagearea network (SAN) storage cluster synchronous disaster recovery. Invarious embodiments, the source storage system and the target storagesystem may each have one or more storage devices and store informationin logical units, e.g., source logical units and target logical units.Further, each of the storage systems may include one or more clusternodes or controllers coupled with the storage devices to form thestorage system. In various embodiments, the cluster nodes may beseparate computing devices and/or controllers for processing read/writerequests for the storage system.

Various embodiments may comprise one or more elements. An element maycomprise any structure arranged to perform certain operations. Eachelement may be implemented as hardware, software, or any combinationthereof, as desired for a given set of design parameters or performanceconstraints. Although an embodiment may be described with a limitednumber of elements in a certain topology by way of example, theembodiment may include more or less elements in alternate topologies asdesired for a given implementation. It is worthy to note that anyreference to “one embodiment” or “an embodiment” means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment. The appearances ofthe phrases “in one embodiment,” “in some embodiments,” and “in variousembodiments” in various places in the specification are not necessarilyall referring to the same embodiment.

The target storage system, in a different site, may be introduced into apreexisting storage system environment, such as a SAN environmentincluding the source storage system. The importation of information fromthe source storage system and source logical unit to the target storagesystem and target logical unit may be initialized. More specifically,the target logical unit may bind with the source logical unit throughone or more cluster nodes and information may be copied from the sourcelogical unit to the target logical unit on a block-by-block basis.

As previously discussed, the storage systems may include one or morecluster nodes. For example, the target storage system may include fourcluster nodes, where each cluster node is paired with another clusternode to form two pairs of cluster nodes. As will be discussed in moredetail below, the paired cluster nodes may form a high availabilitycluster node system such that if one cluster node fails, its pairedcluster node can takeover processing from the failed cluster node.Further, a cluster node may giveback processing to its paired clusternode when it comes back online.

During a failure, takeover or giveback event, one or more modules orcomponents of the storage system may handle the event such that thefailure is transparent to a host device and the importation of data doesnot have to restart from the beginning. For example, when a cluster nodefails, the importation processing may stop or be suspended until thepaired cluster node assumes responsibility of the processes on thefailed cluster node. In addition, any logical units associated withfailed cluster node may be associated with the new cluster node,processes executing on the failed cluster node may be initialized andoperate on the paired cluster node and configuration information may beupdated in memory or a data store. More specifically, configuration oridentification information may be updated such that host deviceread/write requests are sent to the correct cluster node, the pairedcluster node is identified as the current cluster node handling theimportation processing and the location of the logical units associatedwith the paired cluster node is updated.

The described techniques may provide a disaster recovery (DR) solutionfor one or more Vservers within one or more clusters of a SAN. Thesolution may apply to entire clusters or individual Vservers within acluster. In an example, a disaster may occur when one or more Vserversfail and are unable to serve data to the appropriate hosts. In describedembodiments, a secondary Vserver, which has been configured as a backupto a primary Vserver, may be activated during a switchover operation. Inthis manner, when failure occurs, the secondary Vserver may be used toensure that hosts experience little to no disruption in retrieving data.The secondary Vserver may be configured such that hosts see little to nochange at all, and may even be able to use the same volumes and logicalunits (LUNS), for example.

In some embodiments, a secondary Vserver may replicate manyconfiguration items, with identities preserved, of a primary Vserverknown to a host device. In this manner, a host device may access asecondary Vserver in a disaster situation without experiencing delay dueto the disaster. Some identifiers retained by a secondary cluster mayinclude, but are not limited to, SCSI target device World WideIdentifier (WWID), SCSI target WWNN (for fibre channel (FC)) and aniSCSI qualified name (IQN) (for iSCSI), LIF World Wide Port Name (WWPN)(for FC) and tpgtag (for iSCSI), the LIF WWPN (for FC), tpgtag (foriSCSI), rtpid, a LUN serial number, asymmetric logical unit access(ALUA) target port group (TPG) IDs, and/or a LUN ID. Since theseidentities may be preserved, and replicated between primary andsecondary clusters, any data object with a unique identify, such as avolume master set ID (MSID), LIFs WWPN, or LUN serial number, may not bevisible to a host in the primary and secondary cluster simultaneously.To accomplish this, a secondary cluster or Vserver may operate in arestricted state in which it does not serve data. LIFs associated with asecondary Vserver may only be made available when disaster occurs withrespect to a primary Vserver.

To create a seamless experience for a host device accessing data,connectivity between a requesting device, or initiator, and LUNs of alogical storage volume may be retained in a secondary Vserver. In someembodiments, the LUNs may uniquely identify the logical storage volumewithin the context of a virtual storage array. In some embodiments, aninitiator-target-nexus (i-t-n) may identify a target port and may beretained in both the primary and secondary Vserver. In a Fibre Channel(FC) environment, a target port may be identified using a World WidePort Name (WWPN). In an iSCSI environment, a target port may beidentified using an iSCSI Qualified Name (IQN) and a Target Portal GroupTag (TPGT). Initiators may use the target port information foridentification. Thus, a host may not experience data interruption aftera switchover operation, since a LUN serial number and i-t-n value areretained in both primary and secondary Vservers.

FIG. 1 illustrates an embodiment of an operating environment 100 such asmay be associated with various embodiments. As described above, asecondary cluster may be configured to mimic a primary cluster suchthat, during failure, a switchover operation may be performed in arelatively short period of time and hosts requesting data may experiencelittle to no change due to the failure. To accomplish this, someembodiments may configure a SAN to retain the identities of certaindata, as discussed above and below, and may perform other configurationsand metadata handling. Each cluster within a SAN may be designated as asource/primary or destination/secondary and may include one or moremodules. Each module may comprise software and/or hardware, which mayinclude software instructions that, when executed by hardware, such as aprocessor, configure hardware within the cluster.

For example, logical unit (LU) data within SAN 100 may be classifiedinto the following types: LU data, LU configuration data, and LUmetadata. LU data may comprise the host addressable portion of a LU. LUconfiguration data may include LUN specific attributes such as LUNserial number, admin state, or device identification. Otherconfiguration data may also be included based upon differentimplementations. LU configuration data may be stored in a stream linkedoff a base inode of a LUN and in an override storage module in an OOVC.LU configuration data may be modified using one or more managementoperations. LU metadata may include LUN path metadata, which maycomprise persistent reservation, mode pages, and log pages. LU metadatamay be stored in an OOVC.

As shown in FIG. 1, source cluster 103 may store data in one or moreVservers, which may be categorized within SAN 100 as host Vservers ofsubtype “sync-source.” In an embodiment, source cluster 103 may be usedto serve data prior to a disaster or failure of one or more componentswithin source cluster 103. Also illustrated within FIG. 1 is destinationcluster 102, which may host data using one or more Vservers categorizedwithin SAN 100 as subtype “sync-destination.” Destination cluster 102may be used to serve data to one or more hosts after a disaster orfailure of one or more components within source cluster 103. Diskmodules 128, 129 and SCSI Blades 130, 131 may store and execute one ormore modules, such as transport modules, SAN management deamon kernelagents (BCOMKA) modules, and SCSIT modules, for example.

A SAN management deamon (BCOMD) 110, 111 may be a Mhost applicationserver for SAN 100 that manages SAN specific configuration. In addition,BCOMD 110 and 11 may provide a list of SAN tables and table attributesthat may be replicated using a configuration replication module (CRS).In some embodiments, BCOM managed objects may include, but are notlimited to, the following as shown in Table 1:

TABLE 1 UI/Frontend Table Name Backend Table Name fcp fcpConfigfcp_nodename fcpConfig fcp_portname fcpLifTable fcp_wwpnaliaswwpnAliasConfig igroup igroupConfig, initiatorIgroup iscsi iscsiConfigiscsi_nodename iscsiConfig iscsi_alias iscsiConfig iscsi_sessionlif_group_table iscsi_connection lif_group_table tpgroup lif_group_tableiscsi_interface iscsiInterfaceAccessConfig iscsi_accesslistiscsiInterfaceAccessConfig iscsi_security iscsiSecurityConfig lunvdiskIgroupMap map vdiskIgroupMap portset portsetConfig iSCSI ISNSisnsConfig LUN VVOL vdiskBind

Within each managed object, one or more fields may be replicated. Forexample, for each of the following objects (represented by frontendnames), the following fields may be replicated as shown in Table 2:

TABLE 2 UI/Frontend Table Name Replicated Fields fcp vserver,target-name, status-admin fcp_nodename target-name fcp_portname vserver,lif, wwpn fcp_wwpnalias vserver, alias, wwpn igroup vserver, igroup,protocol, ostype, portset, initiator, uuid, alua iscsi vserver,target-name, target-alias, status-admin iscsi_nodename target-nameiscsi_alias target-alias iscsi_session iscsi session showiscsi_connection iscsi connection show iscsi_interface vserver, lit,enabled iscsi_accesslist vserver, initiator-name, lit, alliscsi_security vserver, initiator-name, auth-type, user-name, password,outbound-user-name, outbound-password, clear-outbound, auth-chap-policylun vserver, path, volume, qtree, lun, uuid, vdiskld, igroup, lun-id,lun-id-assigned map vserver, path, volume, qtree, lun, igroup, ostype,protocol, lun-id portset vserver, portset, uuid, port-name, protocoliSCSI ISNS vserver, address, status-admin LUN VVOL vserver,protocol-endpoint-path, vvol-path, protocol-endpoint- identifier,secondary-lun-id, vserver-uuid, protocol-endpoint- msid,protocol-endpoint-vdisk-id, vvol-msid, vvol-vdisk-id, bind-id

Further, BCOMD 110, 111 may stub out configuration operations in a setupphase to prevent cache population. Still further BCOMD 110, 111 mayprovide support for explicit Vserver join and BCOMKA cache populationduring switchover and switchback phases, change all necessary clusterscoped SAN IDs to a Vserver (e.g. tpgtag, alua tpgid), and providesupport for specifying LIF identities, rtpid and alau tpgid at creation.

In an embodiment, Vfmgr module 112 may be configured to manage LIFconfiguration, such as a physical port on which the LIF is hosted, orLIF identities such as IQN and tpgtag and IP address. VLDB modules 114may be configured to track the location of storage volumes with thecluster. DM modules 116 and 117 may be configured as director modules,which may coordinate the transfer of configuration changes due to anadministrator changing a configuration. In addition, DM modules 116 and117 may also handle recovering from errors during CRS transfer.

In an embodiment, a management deamon (MGWD) module 118 may be used by asource Vserver to obtain a list of candidate ports that may be used todetermine destination Vserver FC and iSCSI LIFs. MGWD module 118 mayalso provide an interator that will return a list of home-nodes andhome-ports on which to determine the layout of destination Vserver SANLIFs. To provide a LIF layout, MGWD module 118 may extract sourceVserver configuration data and retrieve a list of FC and iSCSI LIFsalong with their identities. MGWD module 118 may further extractdestination Vserver configuration data, including IP ports in adestination Vserver's IPSpace. Still further, MGWD module 188 may beconfigured to provide customized methods for populating SAN RDB data ata destination cluster.

In an embodiment, MGWD module 119 may be used at a source cluster toobtain a primary Vserver's SAN identify, which may be either WWNN orIQN. MGWD 118, 119 may also be configured to obtain a list of SAN LIFsand identities, obtain fabric names through which a source Vserver's FCPLIFs are connected, and provide any necessary customized methods forextracting SAN RDB data at the source.

In some embodiment, CRS modules 120 and 121 may be configurationreplication modules, which in some embodiments, are responsible fortransferring the configuration changes from one cluster to another asand when they occur. The embodiments are not limited by this example.

In an embodiment, transport module 123 may obtain the name of one ormore fabrics for the source Vserver's FC LIFs. Transport module 122 maybe used to obtain the name of one or more fabrics for which destinationcluster 102 LIFs are connected.

BCOMKA module 125 may be a blocks kernel agent, which may be used bySCSI blades to cache configuration information in the kernel 107. BCOMKAmodule 125 additionally may be configured for pass-through support forobtaining fabric names of the source Verserver's FC LIFs. BCOMKA module124 may be a blocks kernel agent, which may be used by SCSI blades tocache configuration information in the kernel 106. BCOMKA module 124 mayadditionally be configured for pass-through support for obtaining fabricnames through which a destination cluster's FC ports are connected.Further, BCOMKA module 124 may be configured to purge BCOMKA specificdata during a switchback phase.

In an embodiment, SCSIT module 126 may be a SCSI target residing in theSCSI blade. SCSIT module 126 may be used in some embodiments to purgeSCSIT specific data during a switchback phase.

In an embodiment, LIF placement may be performed via interface 151 byextracting relevant configuration information from the primary Vserverusing CRS and/or cross cluster calls. In one example, a LIF placementalgorithm may be used to determine an appropriate home-node andhome-port for each SAN LIF created in a secondary, or source, cluster.The LIF placement algorithm, as described in more detail below, may useconfiguration information from the source and destination clusters, suchas SAN LIF information, FC fabric information, or IP subnet information.Using this information, a LIF placement module may be used to identifythe appropriate node and port for LIFs within a destination Vserver.

In an embodiment, interface 152 may be used to support LIF placementwithin a SAN. For example, relevant configuration information may beobtained from a secondary cluster, such as a list of home-nodes andhome-ports, and may be returned. Other examples of relevantconfiguration information may include ports in a destination Vserver'sIPspace (using a SCON API) and destination fabric names. Thisconfiguration information may be used to determine a list of availablehome-nodes and home-ports, which may be used in conjunction with a LIFplacement algorithm.

Some embodiments may include an interface 153 used to populate adestination cluster in-memory cache. For example, in a switchoveroperation, a SAN API may be used to push SAN RDB data into a BCOMKAcache, SCSIT and transport to enable protocol access.

In an embodiment, one or more caches within a kernel may be purged aftera switchback operation using interface 154. For example, in a switchbackoperation, a CRS may trigger a re-baseline, which may synchronizeupdates from a secondary cluster to a primary cluster. Once complete, apurge of the in-memory cache of a SAN may be initiated using one or moreAPIs within a SAN.

After a switchover operation, a host may access data from a secondarycluster via an interface of data module 128. In this example, it may benecessary to prevent LIFs from a primary cluster from coming online. Ifthat were to occur, the host may begin accessing data from the hostcluster after a switchover has already taken place.

In another embodiment, another interface, as illustrated, may be used topopulate a SAN in-memory cache at a source cluster. A part of aswitchback operation, a SAN API may be invoked on a primary cluster topush SAN RDB data into a BCOMKA cache, SCSIT, and Transport to enableprotocol access.

Some embodiments may include an interface, as illustrated, forpopulating a SAN in-memory cache with LUN attributes. In this manner,LUN attributes may be shared across clusters. Once a volume is mounted,BCOMKA may pull the volume and LUN attributes from VDOM.

In another embodiment, to prevent initiators from seeing LUNs inbatches, a SAN LIF bring-up, or activation, may wait until all mappedLUNs in the Vserver are online. BCOMKA may ensure that all LUN inventoryhas been processed before bring up, or activating, the LIFs.

Operations for the above embodiments may be further described withreference to the following figures and accompanying examples. Some ofthe figures may include a logic flow. Although such figures presentedherein may include a particular logic flow, it can be appreciated thatthe logic flow merely provides an example of how the generalfunctionality as described herein can be implemented. Further, the givenlogic flow does not necessarily have to be executed in the orderpresented unless otherwise indicated. In addition, the given logic flowmay be implemented by a hardware element, a software element executed bya processor, or any combination thereof. The embodiments are not limitedin this context.

FIG. 2 illustrates one embodiment of a logic flow 200, which may berepresentative of the operations executed by one or more embodimentsdescribed herein. At 202, a relationship may be created between primaryand secondary clusters. The relationship may be automatically created byone or more software modules of a distributed computing system, or maybe manually created by a system administrator.

At 204, a command, such as a “metrocluster” enable command, may be run.The command may be initiated by a software module or a systemadministrator. The command may be run on both a primary and secondarycluster, for example. Thereafter, any Vserver that is created within aprimary cluster may be assigned a subtype of “sync-source” and anyVserver that is created within a secondary cluster may be assigned asubtype of “sync-destination.” In some embodiments, such as those usingMCC A/A, Vservers in the primary and secondary clusters may use both“sync-source” and “sync-destination” subtypes. For example, a Vservercreated in a secondary cluster may be assigned a “sync-source” subtypewith a Vserver in a destination cluster being assigned a subtype of“sync-destination.”

At 206, configuration information may be captured from a primary clusterand transferred to corresponding nodes within a secondary cluster.Configuration information may include configuration discussed above andbelow, and may be used to establish a peer environment between Vserverswithin a primary cluster and Vservers within a secondary cluster, asillustrated above with respect to FIG. 1.

At 208, any changes made at a primary cluster may be updated incorresponding nodes of a secondary cluster. Using one or more softwaremodule, executed on, or between, the primary and secondary clusters,changes to configuration information, or stored data, on source Vserversmay be synchronized to corresponding peer destination Vservers.

FIG. 3 illustrates a SAN 300 according to one embodiment. SAN 300 may beconfigured for disaster recovery, such that a primary cluster 302 may bepeered with secondary cluster 303. SAN 300 may include host devices 304and 305, which may be any type of computing system configured to executeone or more applications. Moreover, the host devices 304 and 305 mayinteract with primary cluster 302 and secondary cluster 303 inaccordance with a client/server model of information delivery. That is,the host devices 304 and 305 may request the services of primary cluster302 and secondary cluster 303, and the system may return the results ofthe services requested by the host, by exchanging packets over anetwork. Host devices 304 and 305 may issue packets including file-basedaccess protocols, such as the Common Internet File System (CIFS)protocol or Network File System (NFS) protocol, over TCP/IP whenaccessing information in the form of files and directories. In addition,host devices 304 and 305 may issue packets including block-based accessprotocols, such as the Small Computer Systems Interface (SCSI) protocolencapsulated over TCP (iSCSI) and SCSI encapsulated over Fibre Channel(FCP), when accessing information in the form of blocks.

Each of primary cluster 302 and secondary cluster 303 may include one ormore nodes and Vservers, including cluster storage nodes 310-316 and311-317 and Vservers 318 (including LUN 320), 322 (including LUN 324),319 (including LUN 321), and 323 (including LUN 325). Cluster storagenodes 310-316 and 311-317 and Vservers 318, 322, 319, and 323 may be anycomputing device including a processor, processing circuitry, acontroller, a storage controller, and so forth. Although FIG. 3 onlyillustrates four cluster storage nodes and four Vservers, variousembodiments may include any number of cluster storage nodes andVservers.

Each cluster can make some or all of the storage space on storage nodes310-316 and 311 available to a corresponding host device, such as hostdevices 304 and 305, for example. Host devices may access clusterstorage nodes using well-known protocols, such as Internet SmallComputer System Interface (iSCSI), Fibre Channel Protocol (FCP), orFibre Channel over Ethernet (FCoE). Cluster storage nodes may present orexport data as logical units (LUNs), for example, to host devices 304and 305 via interconnects 350-353 and switches 306-309. In someembodiments, a cluster node 310 can communicate with another clusternode 312 over a cluster interconnect, which can be implement, forexample, as a Gigabit Ethernet switch.

In embodiments, the cluster nodes may be configured as high availabilitypairs (HA). More specifically, cluster nodes 310-312, 314-316, 311-313,and 315-317 may be paired as high availability pairs. The highavailability pairs may provide a redundant failover capability for thestorage system. In various embodiments, each of the cluster nodes mayserve information independently of its paired node during normaloperation. However, in the event of individual cluster node failures,one or more processes for processing data may transfer from the failingor failed cluster node to the surviving paired cluster node. The highavailability pair configuration may protect against hardware failures,including the failure of network interface cards, Fiber ChannelArbitration loops, and shelf input/output modules.

In the high availability pair cluster node environment, each node maymonitor the availability status of its partner by means of a heartbeatsignal that may be transmitted between the cluster nodes through theinterconnects. In various embodiments, the failure to receive aheartbeat signal over interconnects may indicate the paired cluster nodehas failed and trigger a failover or takeover event. In addition to theheartbeat signal, other information may be communicated between thepaired cluster nodes such as, system time, and details concerningtemporary disk unavailability due to pending disk firmware updates.

In an embodiment, cluster nodes may be paired with peer cluster nodes ina secondary storage system. For example, as illustrated, primary cluster302 includes cluster node 310, which may be paired as a disasterrecovery peer with cluster node 311 of secondary cluster 303.

As illustrated within FIG. 3, primary cluster 302 hosts Vserver 318 andsecondary cluster 303 hosts Vserver 323, which are both designated assource servers. As illustrated, each of primary cluster 302 andsecondary cluster 303 include destination Vservers 322 and 319. Asindicated by dashed lines, these destination Vservers may be restrictedduring normal operation, which may restrict the access to them by ahost. Data may not be served during this time and may only resume when adisaster recovery operation is performed and a switchover operation isinitiated.

In an embodiment, hosts 304 and 305 may be connected to primary cluster302 and secondary cluster 303, respectively, via pairs of redundantswitches. For example, switches 306 and 308 may provide a connectionbetween host 304 and primary cluster 302. Switches 307 and 309 mayprovide a connection between host 305 and secondary cluster 303. Inaddition, these switches may be interconnected via inter-switch linkconnections 360 and 362. Each Vserver may also have a series of one ormore LIFs connected to the switches. As shown, LIF 350 is connected toswitch 306, LIF 352 is connected to switch 308, LIF 351 is connected toswitch 307, and LIF 353 is connected to switch 309. In an embodiment,LIF 352 may be used in conjunction with Vserver 322, and thus may beoperationally shut down during periods of normal operation. Likewise,LIF 351, which may be associated with Vserver 323 may be operationallyshut down during normal operation.

A SAN may be configured, as shown in FIG. 3, such that LUNs may beavailable to a host after a failure in a Vserver. This ability providesseveral advantages, which may include the ability to retain theidentifies of specific Vserver SAN objects in a secondary Vserver, hostsmay see the same LIFs in a secondary cluster as a previously usedprimary cluster without the need to change fabric or IP connectivity,zoning, or subnet configurations.

In some embodiments, an optional, but recommended, pre-discovery phasemay be used to discover LUNs. A host may perform pre-discovery during aninitial setup for disaster recovery, either by an administrator of asystem, or software configured to do so. Connections 260 and 362 may beestablished and maintained between primary cluster 302 and secondarycluster 303. For example, host 304 may discover LUN2 325 via LIF s0 andconnection 362 on secondary cluster 303. In a similar manner, host 305may discover LUN1 320 in Vserver 318 via LIF p0 and connection 360 onprimary cluster 302. In this manner, the appropriate information may bepre-discovered prior to a disaster recovery event. Pre-discovery of LUNsmay obviate the need for hosts to attempt discovery after failureoccurs. In addition, pre-discovery may increase the speed at whichrecovery may be made after a disaster event since no reboot may berequired and LUN devices files may be already created.

In some embodiments, LIF placement is used to identify LIFs in asecondary cluster to achieve some of the advantages described above. Forexample, for each LIF within a SAN in a source Vserver, a LIF may becreated in a destination Vserver. By way of example, for each LIF inprimary cluster 302, a LIF may be created in secondary cluster 303. Inthis manner, upon a disaster or failure, hosts may see the same datawithout the need to reconfigure. In an exemplary embodiment, LIFsettings may be maintained between clusters. A LIF identity, such asWWPN, tpgtag, rtpid, or ALUA tpgid may be maintained across clusters,for example.

Other requirements for LIF placement may include connecting each nodewithin primary cluster 302 and secondary cluster 303 with a commonfabric. In this manner, upon completion of a switchover operation,aggregates owned by a node in a primary cluster can easily be owned by apeer in a secondary cluster. In addition, FC LIFs may be zoned on WWPN.

A technique for LIF placement and management may be used within a SAN,such as SAN 300, to accomplish pairing and duplicating LIFs between aprimary cluster 302 and secondary cluster 303. A software module, whichmay include some hardware elements, called an iterator, may beconfigured to return, for each source Vserver SAN LIF, a node and porton a destination Vserver for which a LIF with the same identify can becreated. During a CRS replication phase, the iterator module may priorto SAN LIF creation. Further, the iterator may be configured to returnan error if a suitable node cannot be found.

LIF placement, in some embodiments, may comprise two phases:configuration extraction phase and configuration validation phase. Theextraction phase may extract necessary configuration information from asource Vserver, such as Vserver 318. For source Vservers in FC LIFplacement, configuration may include LIF name, WWPN, adapter type(FC/CAN), rtpid, ALUA TPGID, or fabric name. For source Vservers iniSCSI LIF placement, configuration information may include LIF name, IPaddress, current tpgtag, default tpgtag, rtpif, ALUA TPGID, or adaptertype. (e.g. Ethernet/CNA). For destination Vservers or secondaryclusters in FC LIF placement, configuration information may include afabric name or type of adapter. For destination Vservers in iSCSI LIFplacement, configuration information may include ports in a secondarycluster that are in the same source Vserver IPspace or a type ofadapter. The embodiments are not limited by these examples.

The validation phase may use data from the extraction phase to identifysource nodes and ports, which may be returned to a requestor. Somerequirements may be imposed on these phases, particularly the validationphase. First, LUNs in a secondary Vserver may be required to have thesame number of paths as LUNs in a primary Vserver. Second, LIF to nodemapping may be required at a destination cluster. Among others, thefollowing exemplary rules may be followed when placing LIFs, however,modifications to the below rules based upon different embodiments arepossible:

A SAN may not extract source Vserver zoning information for LIF layouts.

LIF to adapter mappings may be retained at the destination Vserver. Forexample, if a FC LIF is on a FCoE/CNA adapter, the LIF with the sameidentity must use a FCoE/CNA adapter. This may also be required foriSCSI LIFs.

The number of ALUA, AO, and ANO paths should be retained betweendestination and source Vservers.

For FC LIFs, a SAN may provide a list of home nodes and home ports usingthe fabric names as the deciding criterion.

For iSCSI LIFs, the sync-destination Vserver IPspace information may beused to determine the ports that are candidates for iSCSI LIF placement.

LIFs may be placed in a balanced manner from among identified candidatenodes and ports.

FIG. 4 illustrates a logic flow 400 for LIF placement according to oneembodiment. At 402, a SAN LIF may be created on a primary cluster andLIF information corresponding to the new primary cluster LIF may bereplicated by a configuration replication module on a secondary cluster.At this point, in response to a SAN LIF creation code, a LIF placementmodule may be initiated to perform a LIF placement algorithm.

At 404, configuration information, as discussed above, may be extractedfrom a primary cluster using cross cluster calls or by using contents ofa CRS stream.

At 406, a disaster recovery peer node from a secondary cluster that isassociated with the LIF created on the primary cluster at 402 isidentified. Using this information, at 408, ports may be located on anidentified peer node that have the same, or similar, connectivity. Forexample, ports with common fabric names in FC embodiments, or commonsubnet-IPspaces in iSCSI embodiments. If such a port is not found, anerror is returned at 414.

At 410, a returned list of ports may be filtered based upon an adaptertype to obtain a list of candidate ports. At 412, the filtered list maybe used to obtain a port to be used for a secondary cluster LIF. Thechosen port may be chosen based upon a load of all ports, with a portwith the lowest load being chosen. In other embodiments, a port may bechosen such that ports are balanced within the cluster.

FIG. 5 illustrates an embodiment of the present invention in which SAN500 has experienced a failure. In particular, the primary cluster sideof the SAN (indicated by gray shading) has faced a disaster and anentire site failure. While the components of FIG. 5 correspond generallyto like-numbered components of FIG. 3, the illustrated connections havechanged due to the site failure. For example, connections 560, 561, andDR Partner connection have failed. In such a failure, the primarycluster 502 as well as the switches 506 and 508, and host 504 have gonedown due to a disaster. The LIFs on secondary cluster 503 that arepeered with destination Vservers may be brought online into anoperational state. If LUN pre-discovery was performed, as describedabove, active hosts may continue to see the same storage. Prior to aswitchover operation, Vserver 518 included LUN 520, which was exposed byLIFs in primary cluster 502. After a switchover operation, hostsconnected to secondary cluster 503 may access data from Vserver 518using LIF 551, for example.

FIG. 6 illustrates an embodiment of the present invention in which SAN600 has experienced a failure. In particular, the primary cluster sideof the SAN (indicated by gray shading) has faced a disaster and acluster failure. While the components of FIG. 6 correspond generally tolike-numbered components of FIG. 3, the illustrated connections havechanged due to the site failure. For example, connections 660, 661, andDR Partner connection have failed. In such a failure, the primarycluster 602 has gone down due to a disaster, however, unlike FIG. 5,switches 606 and 608 and host 604 remain operable. The LIFs on secondarycluster 503 that are peered with destination Vservers may be broughtonline into an operational state. If LUN pre-discovery was performed, asdescribed above, active hosts may continue to see the same storage.Prior to a switchover operation, Vserver 618 included LUN 620, which wasexposed by LIFs in primary cluster 602. After a switchover operation,hosts connected to secondary cluster 603 may access data from Vserver618 using LIF 651, for example.

In some embodiments, a SAN host may have a timeout for host I/Ooperations (e.g. 60 seconds), after which SCSI initiators start takingrecovery actions. The timeout value may differ for different hosts. Aswitchover operation may be expected to complete in a time period fargreater than the host I/O timeout (e.g. 300 seconds). Thus, a switchovermay become disruptive to some SAN clients.

FIG. 7 illustrates an embodiment of the present invention in which SAN700 has experienced a failure and is in a healing phase. While thecomponents of FIG. 7 correspond generally to like-numbered components ofFIG. 3, the illustrated connections have changed due to the sitefailure, such as connections 760 and 762 being established. A healingphase may be initiated by a module, such as a metrocluster heal-phaseaggrs module. During the healing phase, data is resynchronized betweenprimary and secondary clusters and logs from non-mirrored aggregates maybe replayed. During the healing phase, nodes within the primary clustermay be kept in a power-down state, only keeping storage componentspowered on. At the end of a healing phase, all disaster-stricken clusterstorage may be visible from a surviving cluster and all storage on adisaster stricken site may be repaired. In addition, degraded mirroredaggregates may begin resynchronizing. These functions may all beperformed by a healing module, as described above, which may includesoftware instructions that may be executed by one or more processorswithin SAN 700.

In some embodiments, controller healing may be initiated by ametrocluster heal-phase roots command in which CFO and root aggregatesmay be given back to their respective disaster recovery peered nodes.During a root aggregate healing phase, nodes in a primary cluster 702may be powered on. When these primary cluster nodes are powered up,source Vservers on the primary site may be in a restricted state. Arestricted state Vserver may be configuration locked and may not servedata, ensuring that, at any given time, only one site is serving data tohosts.

A healing phase may result in a disaster stricken site coming backonline, enabling a viewing of all nodes in both primary and secondaryclusters, and source cluster Vservers being in a restricted state.Although root aggregate ownership may change during this process, dataaggregates may still be owned by a secondary site. The secondary clusterserving data for both Vservers 719 and 723. Vservers in the primarycluster, indicated by the shading, may not serve data at this point.

SAN 700 may have different roles during a healing phase depending onwhether a disaster was merely a power loss, or destruction of equipment.In a power loss situation, the source cluster 702 is not destroyed. Asthe nodes of the cluster are booted, one or more logic modules may set abootarg on all the nodes. The Vserver subsystem may not bring upVservers that were previously the primary of a DR peer relationship.Instead, these Vservers are moved into a restricted state. When a BCOMdmodule initializes, it may check the Vserver state. If a restrictedstate is detected, it may ensure that SAN LIFs stay offline and the SANcaches are not populated.

In a destruction, or crater scenario, the primary cluster may bedestroyed. In this scenario, the controllers may be replaced and COT maybe installed on each controller. A new cluster may be recreated and eachnode may join the new cluster. In this manner, the cluster and localnode configuration may be restored from a peer cluster configurationbackup FTP server, which may have been created when the disasterrecovery system was configured. The reconfigured cluster may then bepeered with secondary cluster 703.

FIG. 8 illustrates SAN 800 according to an embodiment in which aswitchback phase has taken place. FIG. 8 is similar to FIG. 3, whichillustrates a steady state. There may be pre-requisites for a switchbackphases to occur, which may include all aggregates being successfullyresynchronized, a completed healing phase, and the disaster-strickensite storage is healed and nodes have been booted. A metroclustercommand, which may be used to show nodes, may display all nodes asenabled at this time.

A switchback may occur according to the following timeline of events. Ata time T0, primary cluster 802 may be down and, after switchover,destination Vservers at secondary cluster 803 may be serving data. At atime T1, one or more nodes on primary cluster 802 may be booted. Also atT1, Vservers at secondary cluster 803 may continue to serve data as aswitchback command is initiated, which will fence off configurationupdates for mcc_dst Vservers, flip the direction of CRS replication, andkickoff CRS re-baseline at a time T2. Also at T2, Vservers at primarycluster 802 may be placed in a restricted state.

At time T3, after RDB replication is completed for all the sourceVservers, a SAN API may be called at SAN 800, which is used to populatea SAN cache for the primary cluster Vservers. During time T3, secondarycluster Vservers may continue to serve data.

At a time T4, a precheck on the primary cluster may take place, whichdetermines whether a switchback operation can be completed. Also at timeT4, Vservers at a secondary cluster continue to serve data.

At a time T5, Ownership of a disk module of the plex may be changed.Volume online notifications may be generated by WAFL to VDOM to a SCSIBlade. BCOMKA may start pulling LUN attrs from VDOM at this time. Alsoat time T5 at the secondary cluster, since storage is pulled while oneor more LIFs are still up, WAFL may return either EOFFLINE or ENOVOLdepending on ops and protocols for I/Os during and after an ownershipchange.

At time T6, volumes and LUn configuration population may be complete ata primary cluster. At this point, SAN 800 may send a notification to theactive job. Also at time T6, the secondary cluster Vservers may continueto serve data on remaining aggregates.

At a time T7, a primary cluster may complete SAN configuration forvolumes and LUNs for a recovering Vserver and the Vserver may berestarted at a time T8. This may repeat for all affected Veservers in aprimary cluster. Also at time T7, secondary cluster Vservers may bemoved to a restricted state. LIFs in the secondary cluster may gooffline at this time. The RTO window (e.g. 120 seconds) may have startedearlier, at time T5, for example, when ownership of the first plex haschanged. A SAN API may also be called to purge SAN caches at time T7. Aspreviously mentioned, at time T8, Vservers at a primary cluster may bestarted. Starting of a Vserver may only proceed once it has beenverified that a corresponding peer Vserver in a secondary cluster is inrestricted state. Also at time T8, all Vservers at a secondary clusterare placed in a restricted state.

It may be noted that between times T7 and T8, SCSI initiators may haveno paths to LUNs in the primary cluster as Vservers are brought online.Thus, it may be desirable to minimize these stages as to cause minimumdisruption to connected hosts.

As discussed above, SAN 800 may play a role during the switchbackprocedure in both primary and secondary clusters. For example, on theprimary cluster, a SAN API may be used to populate SAN caches for sourceservers (mentioned above at time T3). This may result in BCOMKA joiningthe Vserver group on all the nodes. The volume groups may be empty sincethe volumes may not have appeared on a disk module within the primarycluster. When volumes do appear in a disk module (at time T5), WAFL maynotify VDOM, which will in turn notify BCOMKA. SCSIT LU groups may beset up at this time and volume groups may be populated while BCOMKA maypull LUN attributes from VDOM.

In some embodiments, a wipe configuration module (not shown) may beutilized to clear configuration data from nodes in a disaster recoverygroup. Cleared nodes may include a specified node, its HA partner, itsDR peer, and its DR auxiliary. Nodes in a DR group may be disallowedfrom participating in a metrocluster switchover discussed above andstorage failover commands after configuration data has been wiped. Thiscommand may be used to tear down a metrocluster setup and is completewhen the hardware responsible for activating a node, such as a FC-VIadapter, is removed or deactivated. Further, the wipe command may beused to reclaim nodes. In an embodiment, a wipe command may identifyVservers of subtype sync-destination and delete identified Versver'sconfigurations.

FIG. 9 illustrates a SAN 900 according to an embodiment. Before adisaster, a host 902 or 903 may access one or more volumes of a primaryVserver, such as 908 or 909, which are available in a primary plex.After a switchover operation, a host may access the volumes, such as910-916 and 911-917, which have been mirrored on a secondary plex. Asstated above, hosts at the secondary cluster for a Vserver would havepre-discovered LUNs in a primary Vserver. After the switchoveroperation, hosts at the secondary site may see the same LUNs since thetarget and LUN identities may be preserved. In the illustratedembodiments switches 904, 906, 905, and 907 may be either FC or IP.

As illustrated, during normal operation, host 902 may access storage 916via switch 904 and interconnects A during normal operation. Likewise,during normal operation, host 903 may access storage 911 via switch 907and interconnects D. During a failure of site 940, host 903 may accessstorage 913 via switch 905 and interconnects C. During a failure of site950, host 902 may access storage 914 via switch 906 and interconnects B.

FIG. 10 illustrates an embodiment of a storage medium 1000. Storagemedium 1000 may comprise any non-transitory computer-readable storagemedium or machine-readable storage medium, such as an optical, magneticor semiconductor storage medium. In various embodiments, storage medium1000 may comprise an article of manufacture. In some embodiments,storage medium 1000 may store computer-executable instructions, such ascomputer-executable instructions to implement the logic flows describedherein. Examples of a computer-readable storage medium ormachine-readable storage medium may include any tangible media capableof storing electronic data, including volatile memory or non-volatilememory, removable or non-removable memory, erasable or non-erasablememory, writeable or re-writeable memory, and so forth. Examples ofcomputer-executable instructions may include any suitable type of code,such as source code, compiled code, interpreted code, executable code,static code, dynamic code, object-oriented code, visual code, and thelike. The embodiments are not limited in this context.

FIG. 11 illustrates an embodiment of an exemplary computing architecture1100 suitable for implementing various embodiments as previouslydescribed. In various embodiments, the computing architecture 1100 maycomprise or be implemented as part of an electronic device. In someembodiments, the computing architecture 1100 may be used, for example,to implement the systems, logic flows, and articles described herein.The embodiments are not limited in this context.

As used in this application, the terms “system” and “component” and“module” are intended to refer to a computer-related entity, eitherhardware, a combination of hardware and software, software, or softwarein execution, examples of which are provided by the exemplary computingarchitecture 1100. For example, a component can be, but is not limitedto being, a process running on a processor, a processor, a hard diskdrive, multiple storage drives (of optical and/or magnetic storagemedium), an object, an executable, a thread of execution, a program,and/or a computer. By way of illustration, both an application runningon a server and the server can be a component. One or more componentscan reside within a process and/or thread of execution, and a componentcan be localized on one computer and/or distributed between two or morecomputers. Further, components may be communicatively coupled to eachother by various types of communications media to coordinate operations.The coordination may involve the uni-directional or bi-directionalexchange of information. For instance, the components may communicateinformation in the form of signals communicated over the communicationsmedia. The information can be implemented as signals allocated tovarious signal lines. In such allocations, each message is a signal.Further embodiments, however, may alternatively employ data messages.Such data messages may be sent across various connections. Exemplaryconnections include parallel interfaces, serial interfaces, and businterfaces.

The computing architecture 1100 includes various common computingelements, such as one or more processors, multi-core processors,co-processors, memory units, chipsets, controllers, peripherals,interfaces, oscillators, timing devices, video cards, audio cards,multimedia input/output (I/O) components, power supplies, and so forth.The embodiments, however, are not limited to implementation by thecomputing architecture 1100.

As shown in FIG. 11, the computing architecture 1100 comprises aprocessing unit 1104, a system memory 1106 and a system bus 1108. Theprocessing unit 1104 can be any of various commercially availableprocessors, including without limitation an AMD® Athlon®, Duron® andOpteron® processors; ARM® application, embedded and secure processors;IBM® and Motorola® DragonBall® and PowerPC® processors; IBM and Sony®Cell processors; Intel® Celeron®, Core (2) Duo®, Itanium®, Pentium®,Xeon®, and XScale® processors; and similar processors. Dualmicroprocessors, multi-core processors, and other multi-processorarchitectures may also be employed as the processing unit 1104.

The system bus 1108 provides an interface for system componentsincluding, but not limited to, the system memory 1106 to the processingunit 1104. The system bus 1108 can be any of several types of busstructure that may further interconnect to a memory bus (with or withouta memory controller), a peripheral bus, and a local bus using any of avariety of commercially available bus architectures. Interface adaptersmay connect to the system bus 1108 via a slot architecture. Example slotarchitectures may include without limitation Accelerated Graphics Port(AGP), Card Bus, (Extended) Industry Standard Architecture ((E)ISA),Micro Channel Architecture (MCA), NuBus, Peripheral ComponentInterconnect (Extended) (PCI(X)), PCI Express, Personal Computer MemoryCard International Association (PCMCIA), and the like.

The system memory 1106 may include various types of computer-readablestorage media in the form of one or more higher speed memory units, suchas read-only memory (ROM), random-access memory (RAM), dynamic RAM(DRAM), Double-Data-Rate DRAM (DDRAM), synchronous DRAM (SDRAM), staticRAM (SRAM), programmable ROM (PROM), erasable programmable ROM (EPROM),electrically erasable programmable ROM (EEPROM), flash memory, polymermemory such as ferroelectric polymer memory, ovonic memory, phase changeor ferroelectric memory, silicon-oxide-nitride-oxide-silicon (SONOS)memory, magnetic or optical cards, an array of devices such as RedundantArray of Independent Disks (RAID) drives, solid state memory devices(e.g., USB memory, solid state drives (SSD) and any other type ofstorage media suitable for storing information. In the illustratedembodiment shown in FIG. 11, the system memory 1106 can includenon-volatile memory 1110 and/or volatile memory 1112. A basicinput/output system (BIOS) can be stored in the non-volatile memory1110.

The computer 1102 may include various types of computer-readable storagemedia in the form of one or more lower speed memory units, including aninternal (or external) hard disk drive (HDD) 1114, a magnetic floppydisk drive (FDD) 1116 to read from or write to a removable magnetic disk1118, and an optical disk drive 1120 to read from or write to aremovable optical disk 1122 (e.g., a CD-ROM or DVD). The HDD 1114, FDD1116 and optical disk drive 1120 can be connected to the system bus 1108by a HDD interface 1124, an FDD interface 1126 and an optical driveinterface 1128, respectively. The HDD interface 1124 for external driveimplementations can include at least one or both of Universal Serial Bus(USB) and IEEE 1394 interface technologies.

The drives and associated computer-readable media provide volatileand/or nonvolatile storage of data, data structures, computer-executableinstructions, and so forth. For example, a number of program modules canbe stored in the drives and memory units 1110, 1112, including anoperating system 1130, one or more application programs 1132, otherprogram modules 1134, and program data 1136. In one embodiment, the oneor more application programs 1132, other program modules 1134, andprogram data 1136 can include, for example, the various applicationsand/or components of the described systems.

A user can enter commands and information into the computer 1102 throughone or more wire/wireless input devices, for example, a keyboard 1138and a pointing device, such as a mouse 1140. Other input devices mayinclude microphones, infra-red (IR) remote controls, radio-frequency(RF) remote controls, game pads, stylus pens, card readers, dongles,finger print readers, gloves, graphics tablets, joysticks, keyboards,retina readers, touch screens (e.g., capacitive, resistive, etc.),trackballs, trackpads, sensors, styluses, and the like. These and otherinput devices are often connected to the processing unit 1104 through aninput device interface 1142 that is coupled to the system bus 1108, butcan be connected by other interfaces such as a parallel port, IEEE 1394serial port, a game port, a USB port, an IR interface, and so forth.

A monitor 1144 or other type of display device is also connected to thesystem bus 1108 via an interface, such as a video adaptor 1146. Themonitor 1144 may be internal or external to the computer 1102. Inaddition to the monitor 1144, a computer typically includes otherperipheral output devices, such as speakers, printers, and so forth.

The computer 1102 may operate in a networked environment using logicalconnections via wire and/or wireless communications to one or moreremote computers, such as a remote computer 1148. The remote computer1148 can be a workstation, a server computer, a router, a personalcomputer, portable computer, microprocessor-based entertainmentappliance, a peer device or other common network node, and typicallyincludes many or all of the elements described relative to the computer1102, although, for purposes of brevity, only a memory/storage device1150 is illustrated. The logical connections depicted includewire/wireless connectivity to a local area network (LAN) 1152 and/orlarger networks, for example, a wide area network (WAN) 1154. Such LANand WAN networking environments are commonplace in offices andcompanies, and facilitate enterprise-wide computer networks, such asintranets, all of which may connect to a global communications network,for example, the Internet.

When used in a LAN networking environment, the computer 1102 isconnected to the LAN 1152 through a wire and/or wireless communicationnetwork interface or adaptor 1156. The adaptor 1156 can facilitate wireand/or wireless communications to the LAN 1152, which may also include awireless access point disposed thereon for communicating with thewireless functionality of the adaptor 1156.

When used in a WAN networking environment, the computer 1102 can includea modem 1158, or is connected to a communications server on the WAN1154, or has other means for establishing communications over the WAN1154, such as by way of the Internet. The modem 1158, which can beinternal or external and a wire and/or wireless device, connects to thesystem bus 1108 via the input device interface 1142. In a networkedenvironment, program modules depicted relative to the computer 1102, orportions thereof, can be stored in the remote memory/storage device1150. It will be appreciated that the network connections shown areexemplary and other means of establishing a communications link betweenthe computers can be used.

The computer 1102 is operable to communicate with wire and wirelessdevices or entities using the IEEE 802 family of standards, such aswireless devices operatively disposed in wireless communication (e.g.,IEEE 802.16 over-the-air modulation techniques). This includes at leastWi-Fi (or Wireless Fidelity), WiMax, and Bluetooth™ wirelesstechnologies, among others. Thus, the communication can be a predefinedstructure as with a conventional network or simply an ad hoccommunication between at least two devices. Wi-Fi networks use radiotechnologies called IEEE 802.11x (a, b, g, n, etc.) to provide secure,reliable, fast wireless connectivity. A Wi-Fi network can be used toconnect computers to each other, to the Internet, and to wire networks(which use IEEE 802.3-related media and functions).

FIG. 12 illustrates a block diagram of an exemplary communicationsarchitecture 1200 suitable for implementing various embodiments aspreviously described. The communications architecture 1200 includesvarious common communications elements, such as a transmitter, receiver,transceiver, radio, network interface, baseband processor, antenna,amplifiers, filters, power supplies, and so forth. The embodiments,however, are not limited to implementation by the communicationsarchitecture 1200.

As shown in FIG. 12, the communications architecture 1200 comprisesincludes one or more clients 1202 and servers 1204. The clients 1202 andthe servers 1204 are operatively connected to one or more respectiveclient data stores 1208 and server data stores 1210 that can be employedto store information local to the respective clients 1202 and servers1204, such as cookies and/or associated contextual information. Any oneof clients 1202 and/or servers 1204 may implement the apparatuses,systems, methods, and articles described herein in conjunction withstorage of information on any of client data stores 1208 and/or serverdata stores 1210.

The clients 1202 and the servers 1204 may communicate informationbetween each other using a communication framework 1206. Thecommunications framework 1206 may implement any well-knowncommunications techniques and protocols. The communications framework1206 may be implemented as a packet-switched network (e.g., publicnetworks such as the Internet, private networks such as an enterpriseintranet, and so forth), a circuit-switched network (e.g., the publicswitched telephone network), or a combination of a packet-switchednetwork and a circuit-switched network (with suitable gateways andtranslators).

The communications framework 1206 may implement various networkinterfaces arranged to accept, communicate, and connect to acommunications network. A network interface may be regarded as aspecialized form of an input output interface. Network interfaces mayemploy connection protocols including without limitation direct connect,Ethernet (e.g., thick, thin, twisted pair 10/100/1000 Base T, and thelike), token ring, wireless network interfaces, cellular networkinterfaces, IEEE 802.11a-x network interfaces, IEEE 802.16 networkinterfaces, IEEE 802.20 network interfaces, and the like. Further,multiple network interfaces may be used to engage with variouscommunications network types. For example, multiple network interfacesmay be employed to allow for the communication over broadcast,multicast, and unicast networks. Should processing requirements dictatea greater amount speed and capacity, distributed network controllerarchitectures may similarly be employed to pool, load balance, andotherwise increase the communicative bandwidth required by clients 1202and the servers 1204. A communications network may be any one and thecombination of wired and/or wireless networks including withoutlimitation a direct interconnection, a secured custom connection, aprivate network (e.g., an enterprise intranet), a public network (e.g.,the Internet), a Personal Area Network (PAN), a Local Area Network(LAN), a Metropolitan Area Network (MAN), an Operating Missions as Nodeson the Internet (OMNI), a Wide Area Network (WAN), a wireless network, acellular network, and other communications networks.

Various embodiments may be implemented using hardware elements, softwareelements, or a combination of both. Examples of hardware elements mayinclude processors, microprocessors, circuits, circuit elements (e.g.,transistors, resistors, capacitors, inductors, and so forth), integratedcircuits, application specific integrated circuits (ASIC), programmablelogic devices (PLD), digital signal processors (DSP), field programmablegate array (FPGA), logic gates, registers, semiconductor device, chips,microchips, chip sets, and so forth. Examples of software may includesoftware components, programs, applications, computer programs,application programs, system programs, machine programs, operatingsystem software, middleware, firmware, software modules, routines,subroutines, functions, methods, procedures, software interfaces,application program interfaces (API), instruction sets, computing code,computer code, code segments, computer code segments, words, values,symbols, or any combination thereof. Determining whether an embodimentis implemented using hardware elements and/or software elements may varyin accordance with any number of factors, such as desired computationalrate, power levels, heat tolerances, processing cycle budget, input datarates, output data rates, memory resources, data bus speeds and otherdesign or performance constraints.

One or more aspects of at least one embodiment may be implemented byrepresentative instructions stored on a machine-readable medium whichrepresents various logic within the processor, which when read by amachine causes the machine to fabricate logic to perform the techniquesdescribed herein. Such representations, known as “IP cores” may bestored on a tangible, machine readable medium and supplied to variouscustomers or manufacturing facilities to load into the fabricationmachines that actually make the logic or processor. Some embodiments maybe implemented, for example, using a machine-readable medium or articlewhich may store an instruction or a set of instructions that, ifexecuted by a machine, may cause the machine to perform a method and/oroperations in accordance with the embodiments. Such a machine mayinclude, for example, any suitable processing platform, computingplatform, computing device, processing device, computing system,processing system, computer, processor, or the like, and may beimplemented using any suitable combination of hardware and/or software.The machine-readable medium or article may include, for example, anysuitable type of memory unit, memory device, memory article, memorymedium, storage device, storage article, storage medium and/or storageunit, for example, memory, removable or non-removable media, erasable ornon-erasable media, writeable or re-writeable media, digital or analogmedia, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM),Compact Disk Recordable (CD-R), Compact Disk Rewriteable (CD-RW),optical disk, magnetic media, magneto-optical media, removable memorycards or disks, various types of Digital Versatile Disk (DVD), a tape, acassette, or the like. The instructions may include any suitable type ofcode, such as source code, compiled code, interpreted code, executablecode, static code, dynamic code, encrypted code, and the like,implemented using any suitable high-level, low-level, object-oriented,visual, compiled and/or interpreted programming language.

Numerous specific details have been set forth herein to provide athorough understanding of the embodiments. It will be understood bythose skilled in the art, however, that the embodiments may be practicedwithout these specific details. In other instances, well-knownoperations, components, and circuits have not been described in detailso as not to obscure the embodiments. It can be appreciated that thespecific structural and functional details disclosed herein may berepresentative and do not necessarily limit the scope of theembodiments.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. These terms are not intendedas synonyms for each other. For example, some embodiments may bedescribed using the terms “connected” and/or “coupled” to indicate thattwo or more elements are in direct physical or electrical contact witheach other. The term “coupled,” however, may also mean that two or moreelements are not in direct contact with each other, but yet stillco-operate or interact with each other.

Unless specifically stated otherwise, it may be appreciated that termssuch as “processing,” “computing,” “calculating,” “determining,” or thelike, refer to the action and/or processes of a computer or computingsystem, or similar electronic computing device, that manipulates and/ortransforms data represented as physical quantities (e.g., electronic)within the computing system's registers and/or memories into other datasimilarly represented as physical quantities within the computingsystem's memories, registers or other such information storage,transmission or display devices. The embodiments are not limited in thiscontext.

It should be noted that the methods described herein do not have to beexecuted in the order described, or in any particular order. Moreover,various activities described with respect to the methods identifiedherein can be executed in serial or parallel fashion.

Although specific embodiments have been illustrated and describedherein, it should be appreciated that any arrangement calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This disclosure is intended to cover any and all adaptations orvariations of various embodiments. It is to be understood that the abovedescription has been made in an illustrative fashion, and not arestrictive one. Combinations of the above embodiments, and otherembodiments not specifically described herein will be apparent to thoseof skill in the art upon reviewing the above description. Thus, thescope of various embodiments includes any other applications in whichthe above compositions, structures, and methods are used.

It is emphasized that the Abstract of the Disclosure is provided tocomply with 37 C.F.R. § 1.72(b), requiring an abstract that will allowthe reader to quickly ascertain the nature of the technical disclosure.It is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. In addition, inthe foregoing Detailed Description, it can be seen that various featuresare grouped together in a single embodiment for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate preferred embodiment. In theappended claims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein,” respectively. Moreover, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

The invention claimed is:
 1. A method, comprising: configuring a secondvirtual server as a backup to a first virtual server; identifying uniqueidentifiers used by the first virtual server to refer to a first set ofdata objects used by the first virtual server to provide access to avolume; replicating the unique identifiers from the first virtual serverto the second virtual server; applying the unique identifiers to asecond set of data objects of the second virtual server, wherein theunique identifiers refer to both the first set of data objects and thesecond set of data objects, and wherein the second virtual server isconfigured according to a restricted state; and in response todetermining that the first virtual server has failed, performing aswitchover operation to switchover to the second virtual server forproviding access to the volume based upon the second set of dataobjects, wherein the second virtual server is transitioned out of therestricted state.
 2. The method of claim 1, wherein the configuringcomprises: replicating a SCSI target identifier to the second virtualserver.
 3. The method of claim 1, wherein the configuring comprises:replicating a LUN serial number to the second virtual server.
 4. Themethod of claim 1, wherein the configuring comprises: replicating atarget port group identifier to the second virtual server.
 5. The methodof claim 1, wherein the configuring comprises: replicating a LUNidentifier to the second virtual server.
 6. The method of claim 1,wherein the configuring comprises: replicating a port name to the secondvirtual server.
 7. The method of claim 1, wherein the performing theswitchover operation comprises: retaining connectivity between arequesting device through which access to the volume is provided and aLUN of the volume, wherein the connectivity is retained in the secondvirtual server.
 8. The method of claim 7, wherein the LUN identifies thevolume within a context of a virtual storage array.
 9. The method ofclaim 1, wherein the performing the switchover operation comprises:retaining an identifier, of a target port associated with accessing thevolume, in the first virtual server and the second virtual server. 10.The method of claim 1, wherein the configuring comprises: replicating aSAN identity of the first virtual server to the second virtual server.11. A non-transitory machine readable medium comprising instructions forperforming a method, which when executed by a machine, causes themachine to: provide access to a volume through a first virtual server;configure a second virtual server as a backup to the first virtualserver; identify unique identifiers used by the first virtual server torefer to a first set of data objects used by the first virtual server toprovide access to the volume; replicate the unique identifiers from thefirst virtual server to the second virtual server: apply the uniqueidentifiers to a second set of data objects of the second virtualserver, wherein the unique identifiers refer to both the first set ofdata objects and the second set of data objects, and wherein the secondvirtual server is configured according to a restricted state; and inresponse to determining that the first virtual server has failed,perform a switchover operation to switchover to the second virtualserver for providing access to the volume based upon the second set ofdata objects, wherein the second virtual server is transitioned out ofthe restricted state.
 12. The non-transitory machine readable medium ofclaim 11, wherein the instructions cause the machine to: retainconnectivity between a requesting device through which access to thevolume is provided and a LUN of the volume, wherein the connectivity isretained in the second virtual server.
 13. The non-transitory machinereadable medium of claim 12, wherein the LUN identifies the volumewithin a context of a virtual storage array.
 14. The non-transitorymachine readable medium of claim 11, wherein the instructions cause themachine to: retain an identifier, of a target port associated withaccessing the volume, in the first virtual server and the second virtualserver.
 15. The non-transitory machine readable medium of claim 11,wherein the instructions cause the machine to: replicate a SAN identityof the first virtual server to the second virtual server.
 16. Acomputing device comprising: a memory comprising machine executablecode; and a processor coupled to the memory, the processor configured toexecute the machine executable code to cause the processor to: provideaccess to a volume through a first virtual server; configure a secondvirtual server as a backup to the first virtual server; identify uniqueidentifiers used by the first virtual server to refer to a first set ofdata objects used by the first virtual server to provide access to thevolume; replicate the unique identifiers from the first virtual serverto the second virtual server; apply the unique identifiers to a secondset of data objects of the second virtual server, wherein the uniqueidentifiers refer to both the first set of data objects and the secondset of data objects, and wherein the second virtual server is configuredaccording to a restricted state; and in response to determining that thefirst virtual server has failed, perform a switchover operation toswitchover to the second virtual server for providing access to thevolume based upon the second set of data objects, wherein the secondvirtual server is transitioned out of the restricted state.
 17. Thecomputing device of claim 16, wherein the machine executable code causesthe processor to: replicate a SCSI target identifier to the secondvirtual server.
 18. The computing device of claim 16, wherein themachine executable code causes the processor to: replicate a LUN serialnumber to the second virtual server.
 19. The computing device of claim16, wherein the machine executable code causes the processor to:replicate a target port group identifier to the second virtual server.20. The computing device of claim 16, wherein the machine executablecode causes the processor to: replicate a LUN identifier to the secondvirtual server.